Large pipes, known as water mains, deliver water for distribution through smaller diameter mains and pipes to municipal communities. These large mains have diameters typically in the range of 16 to 144 inches, and for special projects up to 252 inches, and convey water under pressure so that water can be eventually delivered under pressure to thousands of faucets and other outlets.
As with other components of infrastructures, water mains are subject to both environmental and use stress, which over time degrade mains to the point of failure. When a water main fails, the results are often catastrophic since millions of gallons of water carry away soil and undermine adjacent surface structures such as roads and, on occasion, buildings. Accordingly, in addition to loss of potable water, which is not inexpensive to accumulate, there is the expense of repairing the mains, filling the holes left by the breaks in the mains and repairing adjacent structures. Repairing, rebuilding and making restitution of damage caused by vast volumes of released waters from a single failure can cost in the range of a few hundred thousand to millions of dollars. As the infrastructure ages, the number of failures occur at an increasing rate, costing municipalities hundreds of millions of dollars every year.
Since water mains are buried, there is currently no effective way to monitor the condition of water main walls from the surface of the ground. While seismic systems can perhaps reveal the location and material composition of a pipe, seismic systems are not sensitive enough to reveal the condition of pipe walls. Radar is also now being used to penetrate the earth's surface and reveal phenomenon beneath the surface but, like sonar, radar signals cannot reveal wall structure. In addition, the soil above a water main can vary composition and can contain other structures such as rocks and assorted debris which interference with the consistency of reflected signals. Since with PCCP there is no leak before a break, which is sudden explosive burst, leak detection technology cannot be used to identify risk conditions that may be developing.
In that current technology has no means for adequately predicting failure by evaluating pipe structure from the surface of the ground, attempts have been made to predict pipe failure by making an evaluation from within the pipe. To date, no effective method or apparatus for doing this has emerged.
The only indicator of eventual pipe failure is the occurrence of a longitudinal crack which appears during the last stages of a progression to pipe failure. This longitudinal crack occurs on the inner surface of the pipe wall and coincides with approximately a breakage of 40 wire turns at the end of the pipe and 100 wire turns mid-length of the pipe. Since there is only a short period of time between the appearance of this longitudinal crack and failure, the occurrence of the crack may be only hours, weeks or perhaps several months before the break. This warning is inadequate in that it conveys nothing about the status of adjoining pipes which may have damage which has progressed to a stage just prior to the appearance of a visual crack.
In view of the aforementioned considerations, there is a need for an arrangement which can evaluate the structure of a water main and predict if, and with some degree of reliability, when a failure will occur, so risk management strategies can be put into place.